I'm testing a new server engine, paperclip, which is a fork of spigot. Has better performance, at least that's the claim. We did notice that mobs don't spawn quite as often, so I've bumped up the spawn rate.
Bukkit default spawnrate is 70 per chunk, and I've raised it to 120. I've also bumped animals and water creatures as well.

As everyone is aware, we occasionally have lag and our TPS drops and we've been spending a LOT of hours on this, trying to solve it. I'm not 100% on what's causing it, but pretty sure it's a few map chunks that have an insane amount of redstone, hoppers, sorters, etc. One build had over 4500 hoppers. I know it's fun to build the automation stuff, but if it causes us lag and we can't solve it from the server side, I will ask to have it redesigned or torn down. If we need to enable different craftbook options to replace some of this complexity, we'll test it and go forward. Also, the number of animals in small areas can cause issues. So, if you have a LARGE animal farm where you are keeping a lot of them, please cull it. By large, anything over 250 or so is too many for one person to reliably use. If you are working on a project where you need a ton of wool, you are free to make the farm bigger, get your wool, then cull the herd back please. Because, if you don't, I will, and you won't get the meat, etc from them.

With the higher spawn rates of animals, you don't need to keep so many locked up. I'll be happy to discuss this with any and everyone, but it boils down to this, if you lag us, that's no fun for anyone. If you insist, you can buy us a bigger server or I'll kill your animals, in front of you, while you are watching!

Effective immediately, I've removed flight from Mining. The world is set to hard, but it's not that hard to fly to get away from mobs or explore chasms.